Manufacture of micaceous insulating materials



Patented Feb. 23, 1954 MANUFACTURE OF MICACEOUS INSULATING MATERIALSJames S. Kilpatrick, Cirencester, England, as=

signer to The Mycalex Company Limited, Cirencester, England, a Britishcompany No Drawing. Application May 1, 1950, Serial No. 159,379

Claims. (Cl. -456) This invention. relates to micaceous insulatingmaterials oi the kind which are formed by mixing low fusing pointvitreous material with powdered mica and heating the mixture so that themica is bonded to the vitreous material at a temperature below the pointof total dehydration. An example of such material is that known underthe registered trade-mark. Mycalex whose manufacture is described interalia in the specification of United States Patent No. 2,303,244.

The object of the present invention is to provide a new form of materialhaving the general character described in the preceding paragraph butwhich possesses, in addition to the dielectric and other advantageousproperties of such material, the capability of being formed into avariety of articles by injection moulding in a more expeditious andeconomical manner than has been possible hitherto with materials of thegeneral class above described.

According to the invention a method of manufacturing a micaceousinsulating material is provided which consists in mixing a white glassfrit with barium carbonate and phlogopite mica, in forming the mixtureinto billets or blocks, in subjecting the billets or blocks to a rise intemperature in a furnace and in moulding and cooling the heat treatedmaterial.

In carrying the invention into effect and in the preferred manner, amixture is prepared consisting of a white glass frit, barium carbonateand phlogopite mica. The frit consisting of cryolite, barium carbonate,potassium carbonate, soda ash and boric acid may be and preferably isformed described in the aforesaid U. S. specification No. 2,303,244.Alternatively, the frit may be prepared from the ingredients in theproportions as follows:

Per cent Barium carbonate 46.75 Boric acid 20.00 Aluminium oxide 0.25Phlogopite mica 33.00

All the ingredients of the mixture are initially ground to a particlesize capable of passing a mesh of 100 x 100 per square inch. Inpreparing the mixture the preferred proportions of the ingredients, thatis of the frit, the barium carbonate and the phlogopite mica, consist inone third of each by weight but, although the proportions may be varied,it has been found essential for the best results in the finishedarticles that the proportions of the frit and the phlogopite mica shouldbe equal. For satisfactory results, the proportions by weight of thefrit and the phlogopite mica should not be greater than 45% of each norless than 30% of each. After thoroughly mixing the said ingredients theyare formed into billets, a small proportion of water being added toassist in forming a coherent body under the moulding pressure.

After formation, as described, the billets are allowed to dry for aperiod up to five days in length. To assist in rendering the materialcoherent and capable of readily forming into billets small proportion ofmethyl cellulose of dextrine may be added to the water and beingvolatile, this added matter disappears when the material is heat treatedas hereinafter described.

After the billets have been dried they are furnace treated to atemperature of the order of degrees C. the time of treatment varyingwith the weight of the billet treated. It has been found in practicethat on the average the time of heat treatment required is about 7minutes per ounce weight of the billet treated. From the furnace thebillets are transferred directly to an injection moulding apparatuswhich may conveniently be of one of the forms described in thespecification of our British Patent No. 601,772. It is essential,however, for satisfactory results to be obtained that the temperature ofthe mould shall be maintained at from 300 to 350 degrees centigrade andthat the moulded articles produced shall be cooled slowly.

The process above described may be modified by including lead oxide inthe proportion of 10% by weight with the barium carbonate, as althoughthis addition adds somewhat to the cost of production, it has theadvantage of enabling the mould temperature to be reduced to one of theorder of 300 degrees centigrade.

The invention possesses the advantage that in comparison with previouslyknown processes for producing an injection moulding material of theMycalex class, the production costs are reduced as are also the powerfactor and the specific gravity of the products. The lowering of thespecific gravity approximately to 2 is an important advantage in thatthe weight of the material, as compared with previous products of asimilar character, is approximately halved for a given volume, therebyrendering the products adapted for aircraft and for other uses whereweight is an important factor.

I claim:

1. The method of manufacturing a micaceous insulating materialcharacterized by its injection moulding properties comprising in mixinga white glass frit with barium carbonate and phlogopite mica, in formingthe mixture into billets or blocks, in subjecting the billets or blocksto a rise in temperature in a furnace and in moulding and cooling theheat treated material said frit, barium carbonate and micabeingeach-employed in the proportion of substantially one-third byweight.

2. The method of manufacturing an article a micaceous insulatingmaterial characterized by its injection moulding properties comprisingin heating a mixture of cryolite, barium carbonate, potassium carbonate,sodaash and *boric acid to form a white glass frit, in mixing said f ritwith barium carbonate and phlogopite mica,in grinding the mixture tofine particle siza in iorrning the ground ingredients into billets under:pressure, in heating said billets and in injection moulding the heattreated material said -frit, barium carbonate andlmica being eachemployed -.in zthe proportion :of substantially one-third :by weight.

:.3. The method according to claim 1 wherein :approximatelytten per centlead oxide isincluded with Ethe zbarium carbonate.

The :methodas defined in claim 2 wherein approximately ten per cent leadoxide is included with the barium carbonate.

5. In the method of manufacturing billets of a micaceous insulatingmaterial suitable for injection moulding, the steps of preparing amixtune of finely ground yvhiteglasslfrit, barium carbonate and-phlogopite mica, the hit and the phlogopite mica being present insubstantially equal proportions, forming the said mixture into1bil1ets1under pressure, allowing the billets to dry ,angl subjectingthe dried billets to heat treatment in a furnace up to a temperature inthe neighbor- "hood of 850 C., -transi1erring the billets from thefurnace to an injection mold maintained at a temperature ofirom 300 to500 C., molding the billets the injection mold, and allowing the'injegtion molded products to cool slowly.

JAMES S. KILPATRICK.

Nam a -Wedlock Feb. 25, 1936 Wed1ock..- .-l- Nov. 2 491 :Number

1. THE METHOD OF MANUFACTURING A MICACEOUS INSULATING MATERIALCHARACTERIZED BY ITS INJECTION MOULDING PROPERTIES COMPRISING IN MIXTUREA WHITE GLASS FRIT WITH BARIUM CARBONATE AND PHLOGOPITE MICA, IN FORMINGTHE MIXTURE INTO BILLETS OR BLOCKS, IN SUBJECTING THE BILLETS OR BLOCKSTO A RISE IN TEMPERATURE IN A FURNACE AND IN MOULDING AND COOLING THEHEAT TREATED MATERIAL SAID FRIT BARIUM CARBONATE AND MICA BEING EACHEMPLOYED ON THE PROPORTION OF SUBSTANTIALLY ONE-THIRD BY WEIGHT.